Question

The action of concentrated sulphuric acid on urea (NH2CONH2) results in the production of a white crystalline solid X of formula H3NO3S. This is a monobasic acid. On treatment with sodium nitrate and dilute hydrochloride acid at 0C it liberates 1 mol of N2 per mol of X, and on addition of aqueous barium chloride the resulting solution yields 1 mol of BaSO4 per mol of X taken. Deduce the structure of X.

Answer 1

NH2CONH2 (Urea) reacts with conc H2SO4 forming X(H3NO3S). X contains one ionisation H (since, X is a monobasic acid). Thus,

X contains free –NH2 as well as free –SO3H. (NaNO2 + HCl) converts free –NH2 into free –OH group liberating N2.

Thus X is NH2 – SO3H (amino sulphonic acid), 1 mol of which liberated 1 mol of N2 on reaction with (NaNO2 + HCl) at 0C and in turn resulting solution gives 1 mol of BaSO4 on reaction with BaCl2